1. Field of the Invention
The present invention relates to a power supply apparatus configured to supply a power supply voltage or otherwise a power supply current to a device under test.
2. Description of the Related Art
A test apparatus includes a power supply apparatus configured to supply a power supply voltage or power supply current (which will be referred to as the “power supply voltage Vdd” hereafter) to a device under test (DUT). FIG. 1 is a block diagram which shows a schematic configuration of a conventional power supply apparatus. A power supply apparatus 1100 includes a power supply output unit 1026 and a frequency controller (which will be referred to as the “controller” hereafter) 1024 configured to control the power supply output unit 1026. For example, the power supply output unit 1026 is configured as an operational amplifier (buffer), a DC/DC converter, a linear regulator, or a constant current source, and is configured to generate a power supply voltage or a power supply current (output signal OUT) to be supplied to the DUT 1.
A decoupling capacitor C1 is arranged in the vicinity of the power supply terminal of the DUT 1. Furthermore, the output terminal of the power supply apparatus 1100 and the power supply terminal of the DUT 1 are connected via a cable. With such an arrangement, the target to be controlled by the power supply apparatus 1100 is not the output signal OUT of the power supply output unit 1026, but in actuality is the power supply voltage Vdd applied to the power supply terminal of the DUT 1. With conventional techniques, the controller 1024 outputs a control value such that the difference between the observed value (control target) that is fed back and a predetermined reference value (standard value) becomes zero. Examples of the observed values include a feedback signal that corresponds to the power supply voltage or the power supply current supplied to the DUT 1. For example, a circuit element 1022 indicated by the subtractor symbol in FIG. 1 is configured as an error amplifier (operational amplifier), and is configured to amplify the difference between the observed value and the reference value. The analog controller 1024 generates a control value such that the difference becomes zero. The state of the power supply output unit 1026 is feedback controlled according to the control value thus generated. As a result, the power supply voltage Vdd to be controlled is stabilized to the target value. The parameters that are to be considered when the control target 1010 is controlled are represented by a parasitic parameter 1030, which is symbolic parameter. The parasitic parameter 1030 includes a parasitic resistance, a parasitic capacitance, a parasitic inductance, and so forth, of the power supply cable and each of the internal components of the power supply apparatus 1100.
With conventional techniques, the controller 1024 is configured employing an analog circuit. Accordingly, the overall performance of the controller 1024 is fixedly determined by the performance of the analog elements that form the analog circuit, which is a problem. That is to say, with a power supply apparatus 1100 designed assuming that the control target 1010 and the parasitic parameter 1030 are both fixed, if either the control target 1010 or the parasitic parameter 1030 differ from what is assumed in the design, such a power supply apparatus 1100 cannot exhibit its design performance.
Furthermore, with conventional techniques, the control target 1010 and the parasitic parameter 1030 are approximated using a well-fitting equivalent circuit. However, such an approximation cannot be expected to provide high precision. In order to solve such a problem, with conventional techniques, in order to provide stabilized circuit operation, there is a need to design the controller 1024 such that it has a narrow feedback bandwidth, which has the undesirable effect of degrading the circuit properties.